Natural gas is widely used to heat homes, generate electricity, and as a basic material used in the manufacture of many types of chemicals. Natural gas, like petroleum oil, is found in large reservoirs underground and must be extracted from these underground reservoirs and transported to processing plants and then to distribution centers for final delivery to the end user. Natural gas is moved with the use of many types and sizes of positive displacement pumps, commonly termed compressors, that collect, pressurize, and push the gas though the distribution pipes to the various processing centers and points of use. These compressors may be located in ships and drilling fields, in chemical and process plants, and in the huge maze of pipes that makeup the distribution network, which brings gas to the market in a pure, useable form.
For transportation and storage, natural gas is compressed to save space. Gas pressures in pipelines used to transport natural gas are typically maintained at 1000 to 1500 psig. To assure that these pressures are maintained, compressing stations are placed approximately 40 to 100 miles apart along the pipeline. This application requires compressors (positive displacement pumps) specifically designed to compress natural gas and occupy a minimal area.
The most common type of positive displacement natural gas compressor is the reciprocating compressor. Reciprocating compressors utilize a pump action that compresses gas by physically reducing the volume of gas contained in a cylinder using a piston. As the cylinder volume filled with gas is decreased through movement of an internal piston, there is a corresponding increase in pressure of the gas in the cylinder.
Reciprocating compressors and fluid pumps benefit from their ease of availability and their modular nature; however, there are limitations that make them less desirable. For instance, compressors and fluid pumps of this type must either be large in size or operate at higher speeds, i.e., rotations per minute (RPM), to produce the necessary pressure and/or volume desired. The increase in size has obvious drawbacks and may preclude use in space limited situations. The increased RPM necessary in physically smaller compressors and fluid pumps produces unwanted side effects such as increased noise as well as increased cost in the form of more expensive parts and/or increased maintenance. Therefore, a need exists for a pump and compressor assembly having a smaller physical footprint that is able to produce the desired pressure and volume while operating at lower RPM.